This invention relates generally to a method for media blasting and finishing a gear or other workpiece or part. The powered part hold-down apparatus of U.S. Pat. No. 5,272,897 may be used for the peening step(s) of the present disclosure, and the disclosure of the U.S. Pat. No. 5,272,897 is hereby incorporated in its entirety by this reference. Elements of other known methods of media blasting and finishing, such as the peen finishing method and apparatus of U.S. Pat. No. 8,453,305, may be used for the present disclosure, and the disclosure of the U.S. Pat. No. 8,453,305 is hereby incorporated in its entirety by this reference.
Media blasting or peening is used to increase the fatigue strength of a gear, workpiece or part. Gears, such as those utilized in automobile transmissions are media blasted to increase their surface durability and ensure that they are suitable for performing their intended functions. As an example, media blasting with steel peening may be used for strengthening the root radius of the teeth of a geared workpiece. The media blasting steps of the present invention includes one or more steps disclosed in U.S. Pat. No. 6,612,909 and the disclosure of the U.S. Pat. No. 6,612,909 patent is hereby incorporated in its entirety by reference.
When media blasting a workpiece, such as a gear, the workpiece is placed in a closed chamber and the blasting system is actuated, whereby media are mixed with air. After mixing of the media and air, a stream of the air/media mixture is directed against the workpiece, often through increased or high-speed application. This process is referred to as peening.
A variety of materials/media may be used for the workpiece, depending on the ultimate application or outcome desired by the workpiece. In automotive applications, it is often desires to increase the strength or hardness of the media in order to have more favorable KSI. In the present disclosure, toughness is discussed in terms of “KSI” (kilo-pound[-force] per square inch) or 1000 psi. KSI is often used in materials science, civil and mechanical engineering to specify stress and Young's modulus. A higher KSI is favorable for materials that will be under larger compressive stresses.
When a workpiece, in particular a workpiece made of media that has a high KSI, is peened, the peening material is blasted against the surface of the workpiece, removing and modifying the microscopic landscape of the surface. When a workpiece includes sharp or distinct edges, such as the tip of a gear tooth, those edges or tips may be unintentionally radiused from the blasting of the peening material, such that a mushroom effect occurs on the edge or tip of the gear tooth. This mushroom effect may alter the operation or functionality of the workpiece. Even if the mushroom effect does not alter the operation or functionality of the workpiece, it may create unwanted noise when the workpiece engages with other components during operation. It is understood that the higher the KSI of a workpiece, the more the tips may be radiused during a peening process.